1. Field of the Invention
This invention relates to a dry grouting agent for injection into porous, water-permeable weak ground so as to make the ground impermeable to water, and to a method of preparing the same.
2. Prior Art Statement
In the dry grouting method, it is generally considered that the diameter of the particles to be injected into the weak ground should be of such size as to enable the particles to penetrate together with the blown-in air into the gaps (30-40.mu.) in a 10 cm-thick layer of standard sand of a mean particle size of 100-300.mu..
To meet this requirement, Japanese Patent Public Disclosure 61(1986)-211417 discloses a method of blowing in ultra-fine cement particles having a mean diameter of not more than 4.mu..
However, even when such ultra-fine cement particles are used, it is difficult to achieve deep penetration into the gaps within the ground because the rough surfaces of the particles prevents them from sliding easily. Moreover, the use of such fine particles disadvantageously makes it necessary to use a high blowing pressure.
In light of these circumstances, a dry grouting agent should preferably contain cement particles which have a diameter of not more than 10.mu., preferably between 2 and 7.mu., which have smooth surfaces and, accordingly, good slipperiness and which nevertheless exhibit the hydrophilic property required for their agglomeration upon contact with water.